We have developed methods to measure insulin binding glucose transport, glucose metabolism and lipolysis in adipocytes isolated from human sucutaneous abdominal tissue. We have found in Pima Indians that measurements of maximum insulin-stimulated glucose transport and metabolism are decreased, and measurements of basal lipolysis are increased in obese subjects with NIDDM compared with measurements in obese glucose tolerance subjects. These alterations are correlated with fasting and two hour postload plasma glucose concentrations suggesting that this in vitro insulin resistance is a reflecting in vivo insulin resistance. Furthermore, we are able to reverse this in vivo insulin resistance concurrent with reversal of in vivo insulin resistance with 3 weeks of insulin therapy. We will follow-up on these findings in a longitudinal study of adult Pima Indians with high and low probabilities of developing diabetes in the next 5 years. Our studies of insulin action in human and rat adipocytes and adipocyte membranes have suggested a role for catecholamines and cyclic AMP in controlling the sensitivity of glucose transport to insulin and a role for substrate control of the glucose transport system. The latter is consistent with the correlation between in vivo glucose concentrations and the in vitro glucose transport rates.